ParseInt() strange octal behavior

Question

I have to convert some input data to integer. I found parseInt() function.
Everything is good if the input is string:

console.log(parseInt("123")) //123

Even if the string starts with 0:

console.log(parseInt("0123")) //123

But if a number starts with 0, it will give 83!

    console.log(parseInt(0123)) //83 instead of 123

I heard about that's because octal behavior (Javascript parseInt() with leading zeros), so I gave a radix parameter to it:

    console.log(parseInt(0123,10)) //83!!!

Still 83!!!

And then, the strangest of all:
I thinked: octal 123 must give 123 in octal! But it gave NaN:

console.log(parseInt(0123, 8)) //NaN

Why this strange behavior?! And how can I fix it?

Thanks!!!

Behavior has nothing to do with `parseInt()`. Try `console.log(0123)` — Patrick Roberts, Dec 22 '18 at 19:39
`parseInt` expects a string. The answer to "how can I fix it?" is to pass the right kind of argument to the function. — Mark, Dec 22 '18 at 19:41

score 2 · Accepted Answer · answered Dec 22 '18 at 19:37

In this code, you can defined a number (rather than a string) in octal format, then passed it to parseInt. Then parseInt casts that number to a string ("83"), and parses it again.

If you pass a string to parseInt you will get the expected result:

console.log(parseInt('0123'))

score 1 · Answer 2 · answered Dec 22 '18 at 19:41

1

You should use a combination of a string and a radix to get the correct value. Here's an example:

parseInt(01234) // returns 668
parseInt('01234', 10) // returns 1234

answered Dec 22 '18 at 19:41

Garrett Kadillak

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There is no information here that isn't already addressed in the existing answer. – Patrick Roberts Dec 22 '18 at 19:42
My answer suggests using the radix as well as a string. – Garrett Kadillak Dec 22 '18 at 19:43
2

But the important part of the question is "why". OP has demonstrated they already know the correct way. You're parroting back to them what they already showed. That doesn't explain why the octal literal is handled differently. – Patrick Roberts Dec 22 '18 at 19:44

ParseInt() strange octal behavior

2 Answers2